Pressure sensitive adhesive for sticking an electromagnetic wave-shielding film and an optically functional film, and a display panel filter element containing same

ABSTRACT

A pressure sensitive adhesive for sticking together an electromagnetic wave-shielding film and an optically functional film, wherein a storage elastic modulus at 70° C. is 7.00×10 4  Pa or more; and a display panel filter element comprising
     (1) an electromagnetic wave-shielding film, the film being a laminate of a transparent substrate film, an adhesive for a metal foil, which is applied on one surface of the transparent substrate film, and a metal foil mesh formed on the adhesive for a metal foil,   (2) a layer of the pressure sensitive adhesive according to (1), which is applied so as to cover the metal foil mesh of the electromagnetic wave-shielding film, and   (3) an optically functional film provided on the pressure sensitive adhesive, are provided. The pressure sensitive adhesive exhibits a sufficient adhesive strength, can be filled into the inside of the pores of the metal foil mesh, and does not generate bubbles in a heating treatment.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a pressure sensitive adhesive forsticking an electromagnetic wave-shielding film and an opticallyfunctional film, and a display panel filter element containing the same.The pressure sensitive adhesive according to the present invention canbe used for the manufacture of a display panel filter elementconstituting, for example, a plasma display panel or the like.

2. Description of the Related Art

It is believed that an electromagnetic wave emitted from anelectromagnetic device such as a plasma display affects not only otherelectromagnetic devices, but also the human body. Particularly, anelectromagnetic wave having a frequency of 30 MHz to 130 MHz is emittedfrom a plasma display, and may affect computers and computer peripheralspositioned therearound. Accordingly, the emitted electromagnetic waveshould be prevented from leaking toward the outside. An electromagneticwave may be shielded, for example, by a method of covering an emittingsource with a case formed from a highly conductive material, or a methodof applying a conductive net on the emitting source. However, anapparatus such as a plasma display, which must be observed, requirestransmittability, and the above methods cannot be adopted.

Therefore, in a plasma display or the like, an electromagneticwave-shielding sheet composed of a transparent substrate film and ametal foil mesh carried thereon via an adhesive layer is used as a meanshaving not only transmittability but also a property of shielding anelectromagnetic wave. The metal foil mesh is formed by mounting a metalfoil on the transparent substrate film via the adhesive layer, andforming pores by etching the metal foil. The electromagneticwave-shielding film, which is a laminate of the transparent substratefilm, the adhesive layer, and the metal foil mesh, can provide arequired shielding property by appropriately adjusting a thickness ofthe metal foil or a size of the mesh pores, even if the strength of anemitted electromagnetic wave is high as in a plasma display. Further, italso has a sufficient transparency to assure a visibility of the displayscreen (see, for example Patent Document No. 1).

The electromagnetic wave-shielding film is stuck together with variousoptically functional films, such as a near infrared light-absorbingfilm, an ultraviolet light-absorbing film, or an antireflective film bya pressure sensitive adhesive applied onto the metal foil mesh on thesurface of the electromagnetic wave-shielding film. After stickingtogether the electromagnetic wave-shielding film and the opticallyfunctional film, an autoclaving treatment is generally carried out undera pressure of about 0.3 to 1.5 MPa at about 40 to 80° C. In theautoclaving treatment as above, the inside of the pores of the metalfoil mesh having a fine concave-convex surface structure is entirelyfilled with the pressure sensitive adhesive under pressure, to entirelyexclude bubbles; this property will be hereinafter sometimes referred toas the “filling-in property”. Further, the pressure sensitive adhesiveused in the above sticking must have a sufficient adhesive strengthbetween the metal foil mesh on the surface of the electromagneticwave-shielding film and the optically functional film, and a sufficientadhesive strength between the optically functional film and the adhesivelayer (for the metal foil) exposed in the pores of the metal foil meshso that a separation of the electromagnetic wave-shielding film from theoptically functional film is prevented.

-   [Patent Document No. 1] Japanese Unexamined Patent Publication No.    2003-188576.

SUMMARY OF THE INVENTION

However, pressure sensitive adhesives conventionally used to sticktogether the electromagnetic wave-shielding film and various opticallyfunctional films have defects in that the adhesive strength isinsufficient, it does not entirely fill the inside of the pores of themetal foil mesh under pressure, or bubbles are generated during a heattreatment.

The inventors of the present invention found that, in the particularapplication of a pressure sensitive adhesive for sticking together anelectromagnetic wave-shielding film and an optically functional film, ahigh adhesive strength can be obtained by adjusting viscoelasticparameters of the pressure sensitive adhesive within a particular scope.

Accordingly, the object of the present invention is to provide apressure sensitive adhesive which exhibits a sufficient adhesivestrength, can be entirely filled into the inside of the pores of themetal foil mesh under pressure, and does not generate bubbles during aheat treatment, in the sticking together of an electromagneticwave-shielding film and various optically functional films.

Other objects and advantages of the present invention will be apparentfrom the following description.

In accordance with the present invention, there is provided a pressuresensitive adhesive for sticking together an electromagneticwave-shielding film and an optically functional film, wherein a storageelastic modulus at 70° C. is 7.00×10⁴ Pa or more.

In accordance with a preferable embodiment of the pressure sensitiveadhesive of the present invention, a storage elastic modulus at 23° C.is 1.00×10⁵ Pa or more.

In accordance with another preferable embodiment of the pressuresensitive adhesive of the present invention, a peak temperature of losstangent (tan δ) is −15° C. or more.

In accordance with still another preferable embodiment of the pressuresensitive adhesive of the present invention, it comprises an acryliccopolymer containing (meth)acrylic alkyl ester monomers, and optionallyfurther containing nitrogen-containing vinyl monomers, as comonomers. Inaccordance with still another preferable embodiment, the acryliccopolymer does not contain an acid comonomer.

Further, the present invention also relates to a display panel filterelement comprising

-   (1) an electromagnetic wave-shielding film, the film being a    laminate of a transparent substrate film, an adhesive for a metal    foil, which is applied on one surface of the transparent substrate    film, and a metal foil mesh formed on the adhesive for a metal foil,-   (2) a layer of the pressure sensitive adhesive, which is applied so    as to cover the metal foil mesh of the electromagnetic    wave-shielding film, and-   (3) an optically functional film provided on the pressure sensitive    adhesive.

The pressure sensitive adhesive of the present invention can be entirelyfilled into the inside of the pores of the metal foil mesh under heatingand pressed, and has a durability under an elevated temperature and ahigh humidity condition, by adjusting the storage elastic modulus at anautoclaving treatment of 70° C. within a particular scope.

The pressure sensitive adhesive of the present invention also has ahigher storage elastic modulus at a normal temperature of 23° C. incomparison with conventional pressure sensitive adhesives, andtherefore, exhibits good adhesive properties to the surface of the metalfoil mesh on the electromagnetic wave-shielding film.

Further, the pressure sensitive adhesive of the present invention has anexcellent corrosion resistance, and therefore, the metal foil mesh isnot corroded when applied on the electromagnetic wave-shielding film.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A pressure sensitive adhesive has viscoelasticity, and thus shows aviscous behavior and an elastic behavior. As viscoelastic parametersquantitatively representing viscoelasticity, the storage elastic modulus(G′), loss elastic modulus (G″), and loss tangent (tan δ) are widelyused. The storage elastic modulus is defined as a ratio of elasticstresses at the same phase of strain, and is associated with acapability of the material to elastically store an energy. The losselastic modulus is a ratio at a different phase of strain, andcorresponds to a capability of the material to dissipate a stress asheat. Further, the ratio (G″/G′) of the above elastic moduli is definedas a loss tangent (tan δ), and represents a ratio of a viscous componentto an elastic component in the material. These viscoelastic parameterscan be determined by an apparatus for measuring dynamic viscoelasticity.

The storage elastic modulus at 70° C. of the pressure sensitive adhesiveof the present invention is 7.00×10⁴ Pa or more, preferably 8.00×10⁴ Paor more, more preferably 9.00×10⁴ Pa or more. The temperature of 70° C.is a typical temperature at which an electromagnetic wave-shielding filmand an optically functional film are stuck together in an autoclave. Ifthe storage elastic modulus (G′) at 70° C. is less than 7.00×10⁴ Pa,durability in the particular application according to the presentinvention may be deteriorated under an elevated temperature and a highhumidity. An upper limit of the storage elastic modulus (G′) at 70° C.does not exist. In the particular application according to the presentinvention, however, if the pressure sensitive adhesive becomes too hard,the pressure at the autoclaving treatment must be increased so that thepressure sensitive adhesive is applied over the metal foil mesh on thesurface of the electromagnetic wave-shielding film, and the inside ofthe pores of the metal foil mesh having a fine concave-convex surfacestructure is entirely filled with the pressure sensitive adhesive. Inthis regard, the upper limit of the storage elastic modulus at 70° C.may be preferably 1.00×10⁶ Pa.

The storage elastic modulus (G′) at 23° C. of the pressure sensitiveadhesive of the present invention is preferably 1.00×10⁵ Pa or more,more preferably 1.50×10⁵ Pa or more, most preferably 2.00×10⁵ Pa ormore. If the storage elastic modulus (G′) at 23° C. is less than1.00×10⁵ Pa, the adhesive strength between the electromagneticwave-shielding film and the optically functional film may beinsufficient in the particular application according to the presentinvention. There is not a particular upper limit of the storage elasticmodulus (G′) at 23° C. In the particular application according to thepresent invention, however, if the storage elastic modulus at 23° C.(G′) becomes too high, the sticking abilities are reduced. In thisregard, the upper limit of the storage elastic modulus at 23° C. may bepreferably 1.00×10⁶ Pa.

The peak temperature of loss tangent (tan δ) of the pressure sensitiveadhesive of the present invention is preferably −15° C. or more, morepreferably −12° C. or more. If the peak temperature is less than −15°C., it might be difficult to obtain a desired adhesive strength. Thereis not a particular upper limit of the peak temperature of loss tangent(tan δ). However, if the peak temperature of loss tangent becomes toohigh, sticking abilities are reduced. In this regard, the upper limit ofthe peak temperature of loss tangent may be preferably 30° C.

The adhesive strength of the pressure sensitive adhesive of the presentinvention is preferably 20 to 50 N/25 mm, more preferably 22 to 45 N/25mm, under the conditions shown in Examples as mentioned below.

A preferable example of the pressure sensitive adhesive of the presentinvention is an acrylic copolymer containing (meth)acrylic alkyl estermonomers as a comonomer, particularly an acrylic copolymer containing(meth)acrylic alkyl ester monomers and nitrogen-containing vinylmonomers as a comonomer. A ratio of the nitrogen-containing vinylmonomers to all the comonomers contained the acrylic copolymer ispreferably 0.1-30.0% by mass, more preferably 3-30% by mass, mostpreferably 4-25% by mass. Hereinafter, a mixture of monomersconstituting the acrylic copolymer is referred to as a monomer mixture.If an amount of the nitrogen-containing vinyl monomers used is less than0.1% by mass, the adhesive strength may become extremely low. If anamount of the nitrogen-containing vinyl monomers used is more than 30%by mass, the filling-in property may be deteriorated.

The (meth)acrylic alkyl ester monomer is, for example, an alkyl acrylateor alkyl methacrylate containing an alkyl ester moiety having 1 to 20carbon atoms, preferably 1 to 12 carbon atoms. Specifically, there maybe mentioned methyl(meth)acrylate, ethyl(meth)acrylate,propyl(meth)acrylate, n-butyl(meth)acrylate, iso-butyl(meth)acrylate,t-butyl(meth)acrylate, pentyl(meth)acrylate, hexyl(meth)acrylate,cyclohexyl(meth)acrylate, 2-ethylhexyl(meth)acrylate,isooctyl(meth)acrylate, decyl(meth)acrylate, dodecyl(meth)acrylate,myristyl(meth)acrylate, palmityl(meth)acrylate, orstearyl(meth)acrylate. The (meth)acrylic alkyl ester monomer as abovemay be used alone or in combination thereof.

One or more of the (meth)acrylic alkyl ester monomer as above may beused at an amount of preferably 70-97% by mass, more preferably 75-95%by mass, in the monomer mixture. If the amount of the (meth)acrylicalkyl ester monomer is less than 70% by mass, the filling-in propertymay be deteriorated. If an amount of the (meth)acrylic alkyl estermonomer is more than 97% by mass, the adhesive strength may becomeextremely low.

It is preferable that the monomer mixture, which is a mixture ofconstitutional components of the acrylic copolymer, further containsmonomers containing one or more cross-linking functional groups in amolecule. The cross-linking functional group may be, for example, ahydroxyl group, an amide group, an amino group, a carboxyl group, or acarbon-carbon unsaturated bond. A hydroxy group, an amide group, anamino group or a carboxyl group is reacted with a cross-linking agent toform a cross-linked structure, whereas an addition reaction ofcarbon-carbon unsaturated bonds forms a cross-linked structure. As themonomer containing a cross-linking functional group in a molecule, theremay be mentioned, for example, a hydroxyalkyl(meth)acrylate, such as2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate,3-hydroxypropyl(meth)acrylate, 2-hydroxybutyl(meth)acrylate,3-hydroxybutyl(meth)acrylate, 4-hydroxybutyl(meth)acrylate; anacrylamide, such as acrylamide, methacrylamide, N-methyl acrylamide,N-methylmethacrylamide, N-methylolacrylamide, N-methylolmethacrylamidea monoalkylaminoalkyl(meth)acrylate, such asmonomethylaminoethyl(meth)acrylate, monoethylaminoethyl(meth)acrylate,monomethylaminopropyl(meth)acrylate, monoethylaminopropyl(meth)acrylate

n ethylenic unsaturated carboxylic acid, such as acrylic acid,methacrylic acid, crotonic acid, maleic acid, itaconic acid, citraconicacid. The monomer containing a cross-linking functional group in amolecule as above may be used alone or in a combination thereof. Thegroup containing one or more carbon-carbon unsaturated bonds is forexample a (meth)acryloyl group. Preferably, the cross-linking functionalgroup-containing monomer does not contain an acid component, from astandpoint of a suppression of corrosion of the metal foil mesh, andthus, hydroxyalkyl (meth)acrylate is particularly preferable.

The cross-linking functional group-containing monomer can be used at anamount of, preferably 0-10% by mass, more preferably 0.2-5% by mass, inthe monomer mixture.

As the nitrogen-containing vinyl monomer, there may be mentioned, forexample, (meth)acrylamide, N-tert-butylacrylamide, N-vinylpyrrolidone,N,N-dimethylacrylamide, N,N-diethylacrylamide,N,N-dimethylaminopropylacrylamide, N-isopropylacrylamide,N-phenylacrylamide, dimethylaminopropylacrylamide, N-vinylcaprolactam,acryloyl morpholine, dimethylaminoethyl acrylate, or acryloylpiperidine.

Of these vinyl monomers as above, it is preferable to use anitrogen-containing vinyl monomer having a glass-transition temperature(Tg) of 80° C. or more, more preferably 110° C. or more as aglass-transition temperature of a corresponding homopolymer. As anexample of such a nitrogen-containing vinyl monomer, there may bementioned acrylamide (119° C.), methacrylamide (171° C.),N-tert-butylacrylamide (135° C.), N,N-dimethylacrylamide (119° C.),N,N-dimethylaminopropylacrylamide (119° C.), N-isopropylacrylamide (134°C.), N-phenylacrylamide (160° C.), acryloyl morpholine (145° C.), oracryloylpiperidine (116° C.), and acryloyl morpholine, orN,N-dimethylacrylamide is particularly preferable. The temperature shownin brackets is a glass-transition temperature of the correspondinghomopolymer.

The nitrogen-containing vinyl monomer also may be the cross-linkingfunctional group-containing monomer.

The acrylic copolymer may optionally contain other monomers such asvinyl acetate or styrene, as a comonomer.

The acrylic copolymer can be prepared, for example, by any knownpolymerization methods, such as a solution polymerization or a masspolymerization from the monomer mixture containing the (meth)acrylicalkyl ester monomers and the nitrogen-containing vinyl monomers. Theweight-average molecular weight thereof is preferably about 200 to 1800thousands, more preferably 500 to 1500 thousands.

Preferably, the acrylic copolymer is cross-linked with a cross-linkingagent. As the cross-linking agent, there may be mentioned, for example,a polyisocyanate compound, a metal chelate compound, or an epoxycompound, and the polyisocyanate compound is preferable. As thepolyisocyanate compound, there may be mentioned, for example, a compoundcontaining two or more isocyanate groups, such as, tolylene diisocyanateor a hydride thereof, an adduct of tolylene diisocyanate withtrimethylolpropane, triphenylmethane triisocyanate,methylene-bis-di-phenylisocyanate or a hydride thereof, hexamethylenediisocyanate, an adduct of hexamethylene diisocyanate withtrimethylolpropane, xylylenediisocyanate, an adduct ofxylenediisocyanate with trimethylolpropane, 4,4′-dicyclohexylmethanediisocyanate, or polymerization product thereof. An amount of thecross-linking agent used is not particularly limited, but generally, is0.01 to 10 parts by mass with respect to 100 parts by mass of theacrylic copolymer.

The pressure sensitive adhesive of the present invention may contain, inaddition to the acrylic copolymer as above, for example, a tackifierresin such as petroleum resin, terpene resin, rosin resin,coumarone-indene resin or phenol resin, antioxidant, ultravioletabsorber, light stabilizer, softening agent, anticorrosive agent, orsilane coupling agent or filler, or other appropriate additives, so longas the object of the present invention is not inhibited.

Further, the pressure sensitive adhesive of the present invention cancontain a near infrared ray adsorbing agent, a neon light shieldingagent, dyestuff, pigment or the like to prevent or alleviate an emissionof various optical radiations, such as near infrared ray or neon light,from the plasma display.

As the near infrared ray adsorbing agent, there may be mentioned, forexample, a colorant, such as a colorant of cyanines, thiols, metalcomplexs, an azo compound, polymethines, diphenyl methanes, triphenylmethanes quinines or diimmonium salt. Two or more agents as mentionedabove can be generally used in combination in accordance with thewavelengths of two or more near infrared rays emitted from the plasmadisplay. As the neon light shielding agent, there may be mentioned, forexample, a cyanine compound, a squalium compound, an azomethinecompound, a xanthene compound, or an oxonol compound.

The pressure sensitive adhesive of the present invention is used forsticking together the electromagnetic wave-shielding film and theoptically functional film, as mentioned above. The electromagneticwave-shielding film may be a laminate of

-   (1) a transparent substrate film,-   (2) an adhesive for a metal foil, which is applied on one surface of    the transparent substrate film, and-   (3) a metal foil mesh formed on the adhesive for a metal foil. As    the transparent substrate film, a film of an acrylic resin, a    polycarbonate resin, a polypropylene resin, a polyethylene resin, a    polystyrene resin, a polyester resin, a cellulose resin, a    polysulfone resin, a polyvinyl chloride resin or the like may be    used. Generally, it is preferable to use a film of a polyester resin    such as polyethylene terephthalate resin, in view of its excellent    mechanical strength and high transparency. The thickness of the    transparent substrate film is not particularly limited, but    preferably is about 50 μm to 200 μm in view of the mechanical    strength and a high resistance to bending. If necessary, on one side    or both sides of the transparent substrate film, a corona discharge    treatment can be carried out or one or two easy-to-adhere pressure    sensitive adhesive layers can be provided.

The electromagnetic wave-shielding film can be prepared, for example, bya method comprising placing a metal foil on one surface of a transparentsubstrate film carrying thereon an adhesive for a metal foil, andetching the metal foil to form a metal foil mesh. As a metal foil, theremay be mentioned a foil of a metal such as copper, iron, nickel, orchromium, or an alloy thereof, or an alloy containing one or moreabove-mentioned metals as main components. The metal foil is notparticularly limited, but a copper foil is preferable because anelectromagnetic wave can be effectively shielded, an etching procedurecan be easily conducted, and the workability is good.

The thickness of the metal foil is preferably 1 μm to 100 μm, morepreferably 5 μm to 20 μm. If the thickness is less than 1 μm, anelectromagnetic wave cannot be sufficiently shielded. If the thicknessis more than 100 μm, side-etching proceeds and cannot be ignored, andthus, it is difficult to form pores in an accurate manner. The metalfoil may have a blackened layer formed by a blackening treatment on theside of the transparent substrate film, to impart not only ananticorrosive property but also an anti-reflective property. A chromatetreatment can be carried out on the blackened layer as an anticorrosivetreatment. When a metal foil without a pre-blackening treatment is used,a blackening treatment can be carried out at any one of the subsequentsteps. The blackened layer also can be formed by forming aphotosensitive resin layer, which may be a resist layer, from ablack-colored composition, carrying out an etching, and allowing theresist layer to remain. Alternatively, a metal plating can be used toform a black coating.

When a film of an ethylene-vinyl acetate copolymer resin having a highthermofusibility or a thermofusible resin such as an ionomer resin isused alone or in combination with another resin film as a laminate, thetransparent substrate film and the metal foil can be laminated withoutan adhesive layer therebetween. In general, however, the lamination iscarried out by a dry laminate method or the like, using an adhesive. Asthe adhesive for a metal foil forming the adhesive layer for a metalfoil, there may be mentioned, for example, an adhesive, such as anacrylic resin, a polyester resin, a polyurethane resin, a polyvinylalcohol resin, a vinyl chloride/vinyl acetate copolymer resin, or aethylene/vinyl acetate copolymer resin. In addition, a thermosettingresin or a radiation-curable resin, such as a ultraviolet ray-curableresin, an electron radiation-curable resin can be used.

The metal foil on the resulting laminate is etched to form thick pores,whereby a mesh is formed. Thus, an electromagnetic wave-shielding film,which is a laminate of the transparent substrate film, the adhesivelayer, and the metal foil mesh can be obtained.

In the electromagnetic wave-shielding film, the metal foil mesh, whichis one of the subjects to be stuck with the pressure sensitive adhesiveof the present invention, is required to have a transmittability, and anaperture ratio of the metal foil mesh used is generally 65 to 95%. Theaperture ratio means a ratio of a transmittable portion without themetal foil to an area of the metal foil mesh. The thickness of the metalfoil mesh is preferably 1 μm to 100 μm, more preferably 5 μm to 20 μm.

The pressure sensitive adhesive of the present invention can be appliedon the side of the metal foil mesh of the electromagnetic wave-shieldingfilm or the surface of the optically functional film by any knownmethods, to thereby form a film carrying the pressure sensitiveadhesive. The pressure sensitive adhesive can be applied, for example,by a method comprising forming a layer of the pressure sensitiveadhesive of the present invention on a releasable surface of the releasesheet by a known applying method, and laying the layer of the pressuresensitive adhesive on the side of the metal foil mesh or the surface ofthe optically functional film to transfer the layer thereto, or a methodcomprising applying the pressure sensitive adhesive on the side of themetal foil mesh or the surface of the optically functional film by aknown applying method. The applying method may be, for example, a rollcoater, a knife coater, a die coater, a blade coater, a gravure coater,a screen printing, or the like.

After the pressure sensitive adhesive of the present invention isapplied on the side of the metal foil mesh of the electromagneticwave-shielding film or the surface of the optically functional film, itis subjected to an autoclaving treatment in the state that it is stuckto the metal foil mesh side and the optically functional film surface.The autoclaving treatment can be carried out by a known method, forexample, at 40 to 80° C., under the pressure of 0.3 to 1.5 MPa.Preferably, the pressure sensitive adhesive is applied at a thicknesssuch that it can entirely cover the metal foil mesh. The thickness ofthe resulting pressure sensitive adhesive after the autoclavingtreatment is preferably 20 μm to 100 μm, more preferably 20 μm to 40 μm.

As the optically functional film, there may be mentioned, for example, afilm absorbing a near infrared or infrared light, a film absorbing aneon light, a film absorbing an ultraviolet light, a film preventing oralleviating a leakage of an electromagnetic wave in addition to themetal foil mesh, a film inhibiting a reflection of an outside light, ora film adjusting a color tone. Further, a film protecting a glasssurface of a display panel, or a film preventing a glass from shatteringalso can be stuck. A substrate of the optically functional film may be afilm of polyethylene terephthalate, polymethyl methacrylate,polycarbonate or the like. The thickness of the substrate is about 20 μmto 300 μm.

The display panel filter element according to the present inventioncomprises

-   (1) the electromagnetic wave-shielding film, the film being a    laminate of-   (a) the transparent substrate film,-   (b) the adhesive for a metal foil, the adhesive (b) being applied on    one surface of the transparent substrate film(a), and-   (c) the metal foil mesh formed on the adhesive (b) for a metal foil,-   (2) the pressure sensitive adhesive, which is applied so as to cover    the metal foil mesh of the electromagnetic wave-shielding film, and-   (3) the optically functional film provided on the pressure sensitive    adhesive.

The display panel filter element can be used as a component of a plasmadisplay panel or the like.

EXAMPLES

The present invention will now be further illustrated by, but is by nomeans limited to, the following Examples.

Example 1

To 200 parts by mass of ethyl acetate, 64.5 parts by mass of n-butylacrylate, 30 parts by mass of methyl acrylate, 0.5 part by mass of2-hydroxyethyl acrylate, and 5 parts by mass of acryloyl morpholine asmonomer components, and 0.2 parts by mass of azobisisobutyronitorile asan initiator were added. The whole was stirred at 60° C. for 17 hours toobtain a solution of acrylate ester copolymer having a weight-averagemolecular weight of 850 thousand. To the resulting copolymer solution, atrifunctional adduct based on xylenediisocyanate [TD-75: manufactured bySoken Chemical & Engineering Co., Ltd.] was added as a cross-linkingagent at an amount of 0.5 part by mass with respect to 100 parts by massof solid content of the copolymer solution. The whole was diluted with2-butanone to a solution having a concentration of 25% by mass, tothereby obtain a solution of a pressure sensitive adhesive. Aglass-transition temperature of acryloyl morpholine homopolymer was 145°C.

The resulting solution of the pressure sensitive adhesive was coated ona releasable surface of a release film [SP-PET3811: manufactured byLINTEC Corporation] by a knife coater, and dried at 90° C. for oneminute to obtain a layer of the pressure sensitive adhesive with athickness of 25 μm. A polyethylene terephthalate film [CosmoshineA4300:manufactured by Toyobo Co., Ltd.] with a thickness of 100 μm waslaminated as a substrate of an optically functional film to obtain afilm carrying the pressure sensitive adhesive.

Example 2

The procedure of Example 1 was repeated, except that 59.5 parts by massof n-butyl acrylate, 30 parts by mass of methyl acrylate, 0.5 part bymass of 2-hydroxyethyl acrylate, and 10 parts by mass of acryloylmorpholine were used as monomer components, to obtain a film carrying apressure sensitive adhesive. A weight-average molecular weight of theresulting acrylate ester copolymer was 850 thousand.

Example 3

The procedure of Example 1 was repeated, except that 54.5 parts by massof n-butyl acrylate, 30 parts by mass of methyl acrylate, 0.5 part bymass of 2-hydroxyethyl acrylate, and 15 parts by mass of acryloylmorpholine were used as monomer components, to obtain a film carrying apressure sensitive adhesive. A weight-average molecular weight of theresulting acrylate ester copolymer was 850 thousand.

Example 4

The procedure of Example 1 was repeated, except that 49.5 parts by massof n-butyl acrylate, 30 parts by mass of methyl acrylate, 0.5 part bymass of 2-hydroxyethyl acrylate, and 20 parts by mass of acryloylmorpholine were used as monomer components, to obtain a film carrying apressure sensitive adhesive. A weight-average molecular weight of theresulting acrylate ester copolymer was 850 thousand.

Example 5

The procedure of Example 1 was repeated, except that 64.5 parts by massof n-butyl acrylate, 30 parts by mass of methyl acrylate, 0.5 part bymass of 2-hydroxyethyl acrylate, and 5 parts by mass of N,N-dimethylacrylamide were used as monomer components, to obtain a film carrying apressure sensitive adhesive. A weight-average molecular weight of theresulting acrylate ester copolymer was 800 thousand. A glass-transitiontemperature of the homopolymer of N,N-dimethyl acrylamide was 119° C.

Example 6

The procedure of Example 1 was repeated, except that 59.5 parts by massof n-butyl acrylate, 30 parts by mass of methyl acrylate, 0.5 part bymass of 2-hydroxyethyl acrylate, and 10 parts by mass of N,N-dimethylacrylamide were used as monomer components, to obtain a film carrying apressure sensitive adhesive. A weight-average molecular weight of theresulting acrylate ester copolymer was 800 thousand.

Example 7

The procedure of Example 1 was repeated, except that 54.5 parts by massof n-butyl acrylate, 30 parts by mass of methyl acrylate, 0.5 part bymass of 2-hydroxyethyl acrylate, and 15 parts by mass of N,N-dimethylacrylamide were used as monomer components, to obtain a film carrying apressure sensitive adhesive. A weight-average molecular weight of theresulting acrylate ester copolymer was 800 thousand.

Example 8

The procedure of Example 1 was repeated, except that 49.5 parts by massof n-butyl acrylate, 30 parts by mass of methyl acrylate, 0.5 part bymass of 2-hydroxyethyl acrylate, and 20 parts by mass of N,N-dimethylacrylamide were used as monomer components, to obtain a film carrying apressure sensitive adhesive. A weight-average molecular weight of theresulting acrylate ester copolymer was 800 thousand.

Example 9

The procedure of Example 1 was repeated, except that 59 parts by mass ofn-butyl acrylate, 30 parts by mass of methyl acrylate, 1 part by mass of2-hydroxyethyl acrylate, and 10 parts by mass of acryloyl morpholinewere used as monomer components, to obtain a film carrying a pressuresensitive adhesive. A weight-average molecular weight of the resultingacrylate ester copolymer was 800 thousand.

Example 10

The procedure of Example 1 was repeated, except that 58 parts by mass ofn-butyl acrylate, 30 parts by mass of methyl acrylate, 2 parts by massof 2-hydroxyethyl acrylate, and 10 parts by mass of acryloyl morpholinewere used as monomer components, to obtain a film carrying a pressuresensitive adhesive. A weight-average molecular weight of the resultingacrylate ester copolymer was 800 thousand.

Example 11

The procedure of Example 1 was repeated, except that 57 parts by mass ofn-butyl acrylate, 30 parts by mass of methyl acrylate, 3 parts by massof 2-hydroxyethyl acrylate, and 10 parts by mass of acryloyl morpholinewere used as monomer components, to obtain a film carrying a pressuresensitive adhesive. A weight-average molecular weight of the resultingacrylate ester copolymer was 800 thousand.

Example 12

The procedure of Example 1 was repeated, except that 54 parts by mass ofn-butyl acrylate, 30 parts by mass of methyl acrylate, 1 part by mass of2-hydroxyethyl acrylate, and 10 parts by mass of acryloyl morpholinewere used as monomer components, to obtain a film carrying a pressuresensitive adhesive. A weight-average molecular weight of the resultingacrylate ester copolymer was 800 thousand.

Comparative Example 1

The procedure of Example 1 was repeated, except that 49.5 parts by massof n-butyl acrylate, 30 parts by mass of methyl acrylate, 20 parts bymass of methyl methacrylate, and 0.5 part by mass of 2-hydroxyethylacrylate were used as monomer components, to obtain a film carrying apressure sensitive adhesive. A weight-average molecular weight of theresulting acrylate ester copolymer was 800 thousand.

Comparative Example 2

The procedure of Example 1 was repeated, except that 79 parts by mass ofn-butyl acrylate, 20 parts by mass of methyl acrylate, and 1 part bymass of 2-hydroxyethyl acrylate were used as monomer components, toobtain a film carrying a pressure sensitive adhesive. A weight-averagemolecular weight of the resulting acrylate ester copolymer was 900thousand.

[Evaluation of Properties] (1) Preparation of a Laminate Film of aCopper Mesh

A copper mesh-laminated film was prepared as an electromagneticwave-shielding film to be used in the following evaluation ofproperties, as follows:

A polyethylene terephthalate film [Cosmoshine A4100: manufactured byToyobo Co., Ltd.] with a thickness of 100 μm was stuck to a copper foilhaving a blackened surface [BW-S: manufactured by Furukawa Circuit FoilCo., Ltd] with a thickness of 10 μm on the surface opposite to theblackened side, with an adhesive based on a polyurethane resin [mixtureof Takelac A310 (main component)/Takenate A10 (curing agent)/ethylacetate=12/1/21 (mass ratio): manufactured by Takeda Pharmaceutical Co.,Ltd.] for a metal foil, to obtain a laminate of the polyethyleneterephthalate film/the layer of the adhesive for a metal foil/the copperfoil.

A resist solution containing casein as a main ingredient was coated onthe copper foil side of the resulting laminate and dried to form aphotosensitive resin layer. A mask with a pattern was used to conduct acontact exposure with an ultraviolet ray. Then, the laminate wasdeveloped with water, cured, and baked at 100° C. to form a resistpattern. The mask used had a pattern with pitches of 300 μm and linewidths of 10 μm. The laminate with the resulting resist pattern wasetched on the resist pattern side by spraying a ferric chloride solution(Baume degree=42; temperature=30° C.), and washed with water. After theresist was removed with an alkali solution, the laminate was washed anddried to obtain a copper mesh laminate, i.e., an electromagneticwave-shielding film, composed of the polyethylene terephthalate film/thelayer of the adhesive for a metal foil/the copper mesh. The apertureratio of the copper foil was 80%, and the thickness of the copper foilwas 10 μm.

(2) Method of Measuring an Adhesive Strength to the Copper Mesh

A sample having a width of 25 mm and a length of 240 mm was cut fromeach of the films carrying the pressure sensitive adhesive. After arelease film was peeled therefrom, the film carrying the pressuresensitive adhesive was stuck to the copper mesh laminate on the coppermesh side. The whole was pressed in an autoclave (manufactured byKurihara Manufactory Inc.) under 0.5 MPa at 70° C. for 30 minutes, andthen allowed to stand at 23° C. under a relative humidity of 50% for 24hours. Thereafter, an adhesive strength was measure by a tensilestrength tester (Tensilon: manufactured by Orientec Co., Ltd.) at apeeling rate of 300 mm/min and a peeling angle of 180°. In all filmsprepared in Examples 1 to 12 and Comparative Examples 1 and 2, thepeeling occurred at an interface between the pressure sensitive adhesiveand the copper mesh.

(3) Method of Measuring an Adhesive Strength to a Glass

The procedure of the above item “(2) Method of measuring an adhesivestrength to the copper mesh” was repeated, except that a non-alkaliglass (1727: manufactured by Corning Inc.) was used instead of thecopper mesh laminate as the adherend.

(4) Method of Measuring a Storage Elastic Modulus (G′) and a LossElastic Modulus (G″)

A specimen having a cylindrical layer (diameter=8 mm and thickness=3 mm)of the pressure sensitive adhesive on a release sheet was prepared bysuccessively laminating thereon layers of the pressure sensitiveadhesive released from a release film carrying thereon a layer(thickness=25 μm) of the pressure sensitive adhesive. Then, a storageelastic modulus (G′) and a loss elastic modulus (G″) were measured by atorsional shear testing method under the following conditions:

-   Measuring apparatus: an apparatus for measuring a dynamic    viscoelasticity [DYNAMIC ANALYZER RDAII: manufactured by Rheometric    Co., Ltd.]-   Frequency: 1 Hz-   Temperature: 23° C., and 70° C.

(5) Method of Calculation of a Loss Tangent (tan δ)

A loss tangent (tan δ) can be calculated from a storage elastic modulus(G′) and a loss elastic modulus (G″) by the following equation:

loss tangent=loss elastic modulus/storage elastic modulus

(6) Existence or Nonexistence of Bubbles

A sample having a width of 50 mm and a length of 120 mm was cut fromeach of the films carrying the pressure sensitive adhesive. After arelease film was peeled therefrom, the film carrying the pressuresensitive adhesive was stuck to the copper mesh laminate on the coppermesh side. The whole was pressed in an autoclave (manufactured byKurihara Manufactory Inc.) under 0.5 MPa at 70° C. for 30 minutes, andthen the existence or nonexistence of bubbles was visually observed. Theresults were evaluated as follows:

∘: No defect in appearance;

x: bubbles existed at an interface between the pressure sensitiveadhesive layer and the copper mesh.

(7) Method of Evaluating Durability

A sample having a width of 50 mm and a length of 120 mm was cut fromeach of the films carrying the pressure sensitive adhesive. After arelease film was peeled therefrom, the film carrying the pressuresensitive adhesive was stuck to the copper mesh laminate on the coppermesh side. The whole was pressed in an autoclave (manufactured byKurihara Manufactory Inc.) under 0.9 MPa at 70° C. for 60 minutes, andthen allowed to stand at 23° C. under a relative humidity of 90% for 24hours, and further, at 80° C. under a relative humidity of 50% for 24hours. Thereafter, the appearance was visually evaluated as follows:

No defect in appearance;

∘: No bubble having a maximum diameter of 100 μm or more was observed;

×: Bubble having a maximum diameter of 100 μm or more was observed.

(8) Method of Evaluating Corrosion Resistance

A sample having a width of 50 mm and a length of 120 mm was cut fromeach of the films carrying the pressure sensitive adhesive. After arelease film was peeled therefrom, the film carrying the pressuresensitive adhesive was stuck to the copper mesh laminate on the coppermesh side. The whole was pressed in an autoclave (manufactured byKurihara Manufactory Inc.) under 0.5 MPa at 70° C. for 30 minutes(pressure conditions 1), or under 0.9 MPa at 70° C. for 60 minutes(pressure conditions 2) to obtain specimens for evaluation. Before andafter the specimen was allowed to stand at 60° C. under a relativehumidity of 90% for 500 hour, transmittances at a wave length of 700 nmwere measured by a spectrophotometer [MPC3100: manufactured by ShimadzuCorp.], and a difference of transmittance rate (ΔY) of the specimen wascalculated. When ΔY was not more than 1.5%, a corrosion resistance wasgood.

(9) Results of Evaluation

The results of the evaluation are shown in the following Table 1.

TABLE 1 Peak Corrosion resistance Corrosion resistance Adhesive Storageelastic temperature (Pressure conditions 1) (Presssure conditions 2)strength (N/25 mm) modulus (Pa) of tan δ ΔY (%) 700 nm ΔY (%) 700 nm oncopper mesh on glass 23° C. 70° C. (° C.) Bubbles Durability 60° C. 90%RH 500 h 60° C. 90% RH 500 h Example 1 22.8 23.0 2.82 × 10⁵ 1.02 × 10⁵−10.0 ◯ ◯ 0.28 0.28 Example 2 25.0 25.0 3.15 × 10⁵ 1.26 × 10⁵ −1.5 ◯ ◯0.40 0.41 Example 3 29.0 34.0 4.56 × 10⁵ 1.56 × 10⁵ 5.0 ◯ ◯ 0.31 0.33Example 4 36.3 36.0 7.47 × 10⁵ 1.33 × 10⁵ 15.0 ◯ ◯ 0.66 0.66 Example 522.0 23.0 2.11 × 10⁵ 7.67 × 10⁴ −11.0 ◯ ◯ 0.34 0.34 Example 6 28.0 25.02.19 × 10⁵ 8.34 × 10⁴ −3.0 ◯ ◯ 0.52 0.55 Example 7 37.5 34.0 3.27 × 10⁵9.66 × 10⁴ 2.7 ◯ ◯ 0.48 0.51 Example 8 41.7 36.0 6.79 × 10⁵ 1.42 × 10⁵10.1 ◯ ◯ 0.51 0.51 Example 9 27.5 20.5 2.55 × 10⁵ 1.12 × 10⁵ −2.0 ◯ ⊚0.25 0.26 Example 10 29.0 19.5 2.74 × 10⁵ 1.32 × 10⁵ −1.0 ◯ ⊚ 0.22 0.21Example 11 41.5 20.5 2.67 × 10⁵ 9.61 × 10⁵ 4.9 ◯ ⊚ 0.34 0.35 Example 1231.0 28.0 4.86 × 10⁵ 1.56 × 10⁵ 17.0 ◯ ⊚ 0.35 0.37 Comparative 25.0 25.01.43 × 10⁵ 5.54 × 10⁴ −3.0 X X 0.38 0.41 Example 1 Comparative 13.4 12.08.28 × 10⁴ 4.46 × 10⁴ −25.0 X X 0.52 0.55 Example 2

The pressure sensitive adhesive of the present invention can be used,for example, in the manufacture of a display panel filter elementconstituting a plasma display panel or the like, and in the manufactureof a display using the same.

As above, the present invention was explained with reference toparticular embodiments, but modifications and improvements obvious tothose skilled in the art are included in the scope of the presentinvention. (24)

1. A pressure sensitive adhesive for sticking together anelectromagnetic wave-shielding film and an optically functional film,wherein a storage elastic modulus at 70° C. is 7.00×10⁴ Pa or more. 2.The pressure sensitive adhesive according to claim 1, wherein a storageelastic modulus at 23° C. is 1.00×10⁵ Pa or more.
 3. The pressuresensitive adhesive according to claim 1, wherein a peak temperature ofloss tangent (tan δ) is −15° C. or more.
 4. The pressure sensitiveadhesive according to claim 1, comprising an acrylic copolymercontaining (meth)acrylic alkyl ester monomers as a comonomer.
 5. Thepressure sensitive adhesive according to claim 4, comprising the acryliccopolymer further containing nitrogen-containing vinyl monomers as acomonomer.
 6. The pressure sensitive adhesive according to claim 4,wherein said acrylic copolymer does not contain an acid comonomer. 7.The pressure sensitive adhesive according to claim 5, wherein saidacrylic copolymer does not contain an acid comonomer.
 8. A display panelfilter element comprising (1) an electromagnetic wave-shielding film,said film being a laminate of a transparent substrate film, an adhesivefor a metal foil, which is applied on one surface of said transparentsubstrate film, and a metal foil mesh formed on said adhesive for ametal foil, (2) a layer of said pressure sensitive adhesive according toclaim 1, which is applied so as to cover said metal foil mesh of saidelectromagnetic wave-shielding film, and (3) an optically functionalfilm provided on said pressure sensitive adhesive.
 9. The display panelfilter element according to claim 8, wherein a storage elastic modulusat 23° C. of said pressure sensitive adhesive is 1.00×10⁵ Pa or more.10. The display panel filter element according to claim 8, wherein apeak temperature of loss tangent (tan δ) of said pressure sensitiveadhesive is −15° C. or more.
 11. The display panel filter elementaccording to claim 8, wherein said pressure sensitive adhesive comprisesan acrylic copolymer containing (meth)acrylic alkyl ester monomers as acomonomer.
 12. The display panel filter element according to claim 11,wherein said pressure sensitive adhesive comprises the acrylic copolymerfurther containing nitrogen-containing vinyl monomers as a comonomer.13. The display panel filter element according to claim 11, wherein saidacrylic copolymer does not contain an acid comonomer.
 14. The displaypanel filter element according to claim 12, wherein said acryliccopolymer does not contain an acid comonomer.